The present invention relates to a method for inspecting completely hermetically sealed packages, such as food and medical consumption articles, for any pinholes.
Today, hermetically sealed packaging is used in a variety of commodities including food and medical consumption articles such as physiological saline to keep their contents in a sterilized state. In the case of food, the presence of pinholes would cause the contents of the package to contact the air, resulting in deterioration or rot. Also, in the case of medical consumption articles, for example, transfusion bottles, the presence of pinholes would cause contamination or deterioration. Thus, the pinhole inspection for these hermetically sealed packages is of great importance.
Conventionally, this pinhole inspection would be carried out in the following method. That is, because a hermetically sealed package does not allow an electrode to be penetrated thereinto, for example in the case of food, a metal pin is stuck into a completed package and taken as one electrode so as to serve as an opposed electrode to an external electrode set in contact with the package. In this state, with a high voltage applied between the two electrodes, the hermetically sealed package is inspected for pinholes, and after the inspection, any pinholes are hermetically sealed in a different process. However, this inspection method has had a drawback that the inspection process would be complicated, requiring a subsequent process of closing the pinholes.
In order that solve this drawback and to allow a pinhole inspection to be done without damaging the completed hermetically sealed package, there has been provided a method for pinhole inspection, for example, in which a food is sandwiched between a pair of electrodes and a voltage is applied a between both electrodes so as to give a large difference between capacitances that are formed between the individual electrodes and the food, respectively. Then, a current which is generated by a spark between one of the electrodes and the food is detected, by which any pinhole is detected (for example, Japanese Patent Publication SHO 50-6998).
When the presence or absence of any pinhole is detected by detecting a current generated by a spark as described above, it would be the actual case in terms of practical work that the presence or absence of pinholes is detected by a change (magnitude) of the detected current. In this case, there may arise an error to the current at the detection point due to some influence of humidity and temperature on the peripheries of the inspection object as well as floating fine dusts or the like, which is the atmosphere in the inspection. As a result, the decision as to the presence or absence of pinholes could not be free from misoperations such as a decision of the presence of a pinhole notwithstanding the absence of any pinhole.
Further, applying a high voltage between the two electrodes that sandwich the hermetically sealed package would cause potential differences to concentrate to weak portions of the electrically insulating film of the hermetically sealed package so that pinholes would be made, thus resulting in a tendency of increasing pinholes. This tendency would have an adverse effect on the inspection package, as a further problem.
The present applicant has previously applied an invention with an aim of preventing the occurrence of misoperations due to the atmosphere in the inspection. In this method, while a hermetically sealed package the contents of which, such as fluid, powder or food having electrical conductivity, are coated with an electrically insulating film is placed on a grounded support electrode of a specified configuration, a DC high voltage is applied between the support electrode and an electrode put into close contact with or opposed proximity to an inspection-object end portion of the hermetically sealed package so that the contents of the hermetically sealed package are electrically charged via a pinhole, if any, present at the inspection-object end portion. Then, the electrode put into contact with the inspection-object end portion is grounded, where a discharge current from the inspection-object end portion is detected, by which the present or absence of any pinhole of the hermetically sealed package is detected (Japanese Patent Applications Nos. HEI 8-53816 and HEI 10-158569).
Using this method has made it possible to fully prevent the occurrence of misoperations without being affected by the atmosphere in the inspection such as humidity and temperature. However, the method has still required a sequence of inspection procedure.
The present invention has been accomplished in view of these and other problems. An object of the present invention is therefore to provide an efficient method for inspecting a hermetically sealed package which method allows the inspection to be achieved with further simpler procedure, which method is fully prevented from occurrences of misoperations due to the atmosphere during the inspection, and further which method never causes pinholes to be made in the hermetically sealed package even if the electrically insulating film has weak portions.
For this method, the hermetically sealed package to be inspected can be exemplified, in the field of food, principally by cylindrical-shaped packages such as sausage hermetically sealed and packaged in unit pieces, and besides retort foods packed in a flat bag made of plastic film. In the field of medical consumption articles, the hermetically sealed package can be exemplified by blood preparations such as transfusion blood and blood plasmas contained in a plastic bag in addition to transfusion agents such as physiological saline or Ringer""s solution contained in a transfusion bottle also made of plastic as the inspection object for prevention of contamination and deterioration of the contents due to contact with outside air via pinholes. High-resistance electrifiable fluids such as distilled water can also be inspected.
Furthermore, hermetically sealed packages in which a particle or powder conductive material such as cooked rice or solid-matter iron powder is hermetically sealed in a plastic bag also can be an object of inspection as well.
In order to achieve the above object the present invention provides a method for inspecting a hemeticauly sealed package, comprising the steps of: electrifying a hermetically sealed package 3 in which contents 1 such as electically conductive fluid or powder or food are covered with an electrically insulating film 2 by putting an electrical conductor 4 namely a single electrode of a pair of voltage output terminals of a DC high voltage power supply 6 into contact with or proximity to a side face portion 31 of the hermetically sealed package 3 so that the contents 1 in the hermetically sealed package 3 are electrified; then, putting an electrode 5 connected to a grounded grounding wire 8 into proximity to or contact with a inspection-object portion 3a; and detecting occurence of light or/and noise due to electric discharge that occurs in a presence of a pinhole at the inspection-object portion 3a to thereby detect any pinhole of hermetically sealed package 3.
As a result of this, when the electrical conductor 4 derived from the voltage output terminal of the DC high voltage power supply 6 is put into contact with or proximity to the side face portion 31 of the hermetically sealed package 3, the electrically conductive contents 1 in the hermetically sealed package 3 are electrified to a negative or positive potential of the DC high voltage (0.6 kV-30 kV) applied to the electrical conductor 4, causing negative (xe2x88x92) ions or positive (+) ions to be generated.
Next, as the electrode 5 connected to the grounded grounding wire 8, it occurs in the presence of a pinhole at the inspection-object portion 3a that if negative (xe2x88x92) ions are generated within the contents 1, the negative (xe2x88x92) ions are concentrated to the pinhole, or that if positive (+) ions are generated within the contents 1, the positive (+) ions are concentrated to the pinhole, where electric discharge occurs between the inspection-object portion 3a and the electrode 5 connected to the grounded grounding wire 8 through the pinhole. This discharge will cause light or/and noise to be generated, and the light or/and noise can be detected by the sensor 7. By this detection, it can be detected that a pinhole is present at the inspection-object portion 3a. 
If no pinhole is present at the inspection-object portion 3a, there will not occur electric discharge, so that neither light or/and noise will not be generated. Accordingly, the sensor 7 will not be activated, which makes it possible to detect that no pinhole is present at the inspection-object portion 3a. In this case, an optical sensor may be used with a view to detecting light which is to be generated by the discharge, a noise sensor may be used with a view to detecting noise which is to be generated by the discharge, and both an optical sensor and a noise sensor may be used with a view to detecting both light and noise.
For the electrode 5, although various forms of electrodes suitable for the inspection-object portion 3a are possible, it is effective to employ an electrically conductive brush made of electrically conductive plastic fiber.
This electrically conductive brush as an electrode 5 may be formed of acrylic fiber impregnated with copper oxide. This electrically conductive brush employs plastic fiber as its base material, being soft in terms of rigidity so as not to damage the inspection object, lending itself to extremely advantageous use as an electrode when its brush shape is formed in accordance with the inspection object.
Also, it is advantageous that the step of detecting the presence or absence of generation of light due to electric discharge that occurs in the presence of a pinhole at the inspection-object portion 3a is a step of letting light emission due to the discharge incident on a photomultiplier tube 72 via an optical fiber 71 to convert the light into electricity by the photomultiplier tube 72, and detecting the electricity by a detector 73. By doing so, even with a weak light emission due to the discharge, the detection can easily be achieved.
In such a case, it is advantageous that the light emission due to the electric discharge is let incident on the optical fiber 71 via an ultraviolet-transmitting, visible-absorption filter 74. By doing so, even if the place is so bright that light is hard to detect, the light emission can easily be detected by detecting only ultraviolet rays generated by the discharge phenomenon. In addition, an optical fiber 71 that allow ultraviolet rays to easily transmit therethrough should be used.
Furthermore, depending on the circumstances, the light emission due to the electric discharge may be let incident on the optical fiber 71 via an ultraviolet-transmitting, visible-absorption filter 74 and an ultraviolet-converting fluorescent glass 75. By doing so, in the case where the inspection-object portion 3a is annular or other shaped, by using an ultraviolet-transmitting, visible-absorption filter 74 and an ultraviolet-converting fluorescent glass 75 both of which are so wide as to cover the annular or other shape, it becomes possible to easily capture electric discharge no matter where in the annular or other shape the electric discharge has occurred, convert only ultraviolet components of the emitted light into fluorescent light, and thus easily detect the light emission.